1. Field of the Invention
The present invention relates to a bonding method and bonding structure between a cemented carbide element and a diamond element. In addition, the present invention relates to a cutting tip, cutting element, and a drilling tool for drilling a well (winze) or the like.
2. Description of the Related Art
Drilling tools are used to drill oil wells and other types of wells. As one such type of drilling tool, a drilling tool is known in which posts made of superhard tungsten carbide alloy (below, referred to as “cemented carbide posts”) are attached to the distal surface of an iron alloy tool body in a predetermined arrangement by methods such as brazing and shrinkage fitting, and cutting tips consisting of ultrahigh pressure sintered diamond (below, referred to as “sintered diamond”) are brazed to each of these cemented carbide posts. The drilling tool is mounted on the distal end of a pipe, the pipe is rotated while applying a weight via the pipe in the drilling direction, and thereby drilling is carried out by the cutting tips provided on the tool body.
Because the wettability of the sintered diamond that forms the cutting tip with respect to the brazing filler metal is low, brazing using a standard brazing filler metal is difficult. In the drilling tool disclosed in Japanese Unexamined Patent Application, First Publication, No. 2000-000686, an Au alloy brazing filler metal (melting point, 940° C.) having a composition including, for example, Cu at 20 to 40% by mass and Ti at 0.5 to 10% by mass, with the remainder consisting of Au and unavoidable impurities, is used in order to braze a cutting tip to a cemented carbide post. In addition, U.S. Pat. No. 6,248,447B1 discloses a drilling tool in which cutting tips are formed by high heat resistant sintered diamond.
In recent years, requirements for labor saving, energy saving, and cost reduction in the drilling operation are increasingly severe. For example, because the operating cost for one day during drilling operations for development drilling for petroleum and the like is extremely high, it is necessary to complete the drilling operation in a short time period by increasing the drilling speed in order to reduce costs.
In order to increase the drilling speed, both the load applied to the tool body and the rotation speed of the tool body should be increased. However, in both of these cases, a heavier load is applied to the cutting tips. The cemented carbide posts made of cemented carbides and the cutting tips made of sintered diamond are bonded by the brazing described above, and this bonding strength is not very high. Therefore, when an extremely heavy load is applied to the cutting tips, the cutting tips may break off from the cemented carbide posts. In addition, when the drilling becomes high-speed, the heat due to drilling becomes high, and thereby it is possible that the cutting tips will break off from the cemented carbide posts because the brazing filler metal used to braze the cutting tip can melt. Thus, conventionally it has not been possible use an extremely high drilling speed.
In consideration of the problems described above, it is an object of the present invention to increase the bonding strength between the cemented carbide element and the diamond element.